A data replicating system which replicates data in case of loss of data accumulated in a database is proposed and in practical use.
For example, it is proposed as a first related technology of the present invention that an application server replicates a data operation request and transmits the same data operation request to a plurality of nodes, each of the nodes processes the same data operation request, so that the data accumulated in the plurality of nodes is equalized (refer to, for example, Patent Literature PTL 1). It is also proposed as a second related technology of the present invention, the target of which is KVS (Key-Value Store) to store replicated same data in the plurality of nodes (refer to, for example, Patent Literature PTL 2).
As a method of reducing a frequency of access to a permanent storage device, which is involved by processing a data operation request, there is an antecedent log writing technique called WAL (Write Ahead Logging). In WAL, the completion of writing a post-update log of a data record is considered to be the completion (commitment) of processing the data operation request, and the actual updating the data record is performed on the basis of the post-update log at the time of subsequent checkpoint. For example, it is proposed as a third related technology of the present invention to adopt WAL for a transaction processing, to write a post-update log to the permanent storage device at the time of commitment of the transaction, and to write actual data to a database at the time of checkpoint (refer to, for example, patent literature 3).